Storage cluster operation using erasure coded data

ABSTRACT

A non-volatile solid-state storage is provided. The non-volatile solid state storage includes a non-volatile random access memory (NVRAM) addressable by a processor external to the non-volatile solid state storage. The NVRAM is configured to store user data and metadata relating to the user data. The non-volatile solid state storage includes a flash memory addressable by the processor. The flash memory is configured to store the user data responsive to the processor directing transfer of the user data from the NVRAM to the flash memory.

This application is a continuation of U.S. Pat. No. 9,836,245 which is incorporated herein by reference for all purposes.

BACKGROUND

Solid-state memory, such as flash, is currently in use in solid-state drives (SSD) to augment or replace conventional hard disk drives (HDD), writable CD (compact disk) or writable DVD (digital versatile disk) drives, collectively known as spinning media, and tape drives, for storage of large amounts of data. Flash and other solid-state memories have characteristics that differ from spinning media. Yet, many solid-state drives are designed to conform to hard disk drive standards for compatibility reasons, which makes it difficult to provide enhanced features or take advantage of unique aspects of flash and other solid-state memory.

It is within this context that the embodiments arise.

SUMMARY

In some embodiments a non-volatile solid-state storage is provided. The non-volatile solid state storage includes a non-volatile random access memory (NVRAM) addressable by a processor external to the non-volatile solid state storage. The NVRAM is configured to store user data and metadata relating to the user data. The non-volatile solid state storage includes a flash memory addressable by the processor. The flash memory is configured to store the user data responsive to the processor directing transfer of the user data from the NVRAM to the flash memory.

Other aspects and advantages of the embodiments will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments.

FIG. 1 is a perspective view of a storage cluster with multiple storage nodes and internal storage coupled to each storage node to provide network attached storage, in accordance with some embodiments.

FIG. 2 is a system diagram of an enterprise computing system, which can use one or more of the storage clusters of FIG. 1 as a storage resource in some embodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storage node and contents of one of the non-volatile solid-state storages in accordance with some embodiments.

FIG. 4 is a block diagram showing a communication path for redundant copies of metadata, with further details of storage nodes and solid-state storages in accordance with some embodiments.

FIG. 5 is a flow diagram of a method for accessing a non-volatile solid-state storage, which can be practiced on or by embodiments of storage clusters, storage nodes and/or non-volatile solid-state storage units in accordance with some embodiments.

FIG. 6 is an illustration showing an exemplary computing device which may implement the embodiments described herein.

DETAILED DESCRIPTION

The embodiments below describe a storage cluster that stores user data, such as user data originating from one or more user or client systems or other sources external to the storage cluster. The storage cluster distributes user data across storage nodes housed within a chassis, using erasure coding and redundant copies of metadata. Erasure coding refers to a method of data protection in which data is broken into fragments, expanded and encoded with redundant data pieces and stored across a set of different locations, such as disks, storage nodes or geographic locations. Flash memory is one type of solid-state memory that may be integrated with the embodiments, although the embodiments may be extended to other types of solid-state memory or other storage medium, including non-solid state memory. Control of storage locations and workloads are distributed across the storage locations in a clustered peer-to-peer system. Tasks such as mediating communications between the various storage nodes, detecting when a storage node has become unavailable, and balancing I/Os (inputs and outputs) across the various storage nodes, are all handled on a distributed basis. Data is laid out or distributed across multiple storage nodes in data fragments or stripes that support data recovery in some embodiments. Ownership of data can be reassigned within a cluster, independent of input and output patterns. This architecture described in more detail below allows a storage node in the cluster to fail, with the system remaining operational, since the data can be reconstructed from other storage nodes and thus remain available for input and output operations. In various embodiments, a storage node may be referred to as a cluster node, a blade, or a server.

The storage cluster is contained within a chassis, i.e., an enclosure housing one or more storage nodes. A mechanism to provide power to each storage node, such as a power distribution bus, and a communication mechanism, such as a communication bus that enables communication between the storage nodes are included within the chassis. The storage cluster can run as an independent system in one location according to some embodiments. In one embodiment, a chassis contains at least two instances of the power distribution and the internal and external communication bus which may be enabled or disabled independently. The internal communication bus may be an Ethernet bus, however, other technologies such as Peripheral Component Interconnect (PCI) Express, InfiniBand, and others, are equally suitable. The chassis provides a port for an external communication bus for enabling communication between multiple chassis, directly or through a switch, and with client systems. The external communication may use a technology such as Ethernet, InfiniBand, Fibre Channel, etc. In some embodiments, the external communication bus uses different communication bus technologies for inter-chassis and client communication. If a switch is deployed within or between chassis, the switch may act as a translation between multiple protocols or technologies. When multiple chassis are connected to define a storage cluster, the storage cluster may be accessed by a client using either proprietary interfaces or standard interfaces such as network file system (NFS), common internet file system (CIFS), small computer system interface (SCSI) or hypertext transfer protocol (HTTP). Translation from the client protocol may occur at the switch, chassis external communication bus or within each storage node.

Each storage node may be one or more storage servers and each storage server is connected to one or more non-volatile solid state memory units, which may be referred to as storage units. One embodiment includes a single storage server in each storage node and between one to eight non-volatile solid state memory units, however this one example is not meant to be limiting. The storage server may include a processor, dynamic random access memory (DRAM) and interfaces for the internal communication bus and power distribution for each of the power buses. Inside the storage node, the interfaces and storage unit share a communication bus, e.g., PCI Express, in some embodiments. The non-volatile solid state memory units may directly access the internal communication bus interface through a storage node communication bus, or request the storage node to access the bus interface. The non-volatile solid state memory unit contains an embedded central processing unit (CPU), solid state storage controller, and a quantity of solid state mass storage, e.g., between 2-32 terabytes (TB) in some embodiments. An embedded volatile storage medium, such as DRAM, and an energy reserve apparatus are included in the non-volatile solid state memory unit. In some embodiments, the energy reserve apparatus is a capacitor, super-capacitor, or battery that enables transferring a subset of DRAM contents to a stable storage medium in the case of power loss. In some embodiments, the non-volatile solid state memory unit is constructed with a storage class memory, such as phase change or other resistive random access memory (RRAM) or magnetoresistive random access memory (MRAM) that substitutes for DRAM and enables a reduced power hold-up apparatus.

The storage nodes have one or more non-volatile solid-state storage units, each of which has non-volatile random-access memory (NVRAM) and flash memory, in some embodiments. The NVRAM and the flash memory are independently addressable by the storage node, or more specifically, by a processor of the storage node. The storage node writes user data into the NVRAM, for storage in the flash memory. The storage node, e.g., the processor of the storage node, also writes metadata into the NVRAM, which is usable as a workspace for the processor. Direct memory access (DMA) is applied to transfer user data from the NVRAM to the flash memory, for storage of the user data. DMA is also applied to transfer contents of the NVRAM to the flash memory in case of power loss. In some embodiments, a controller in the non-volatile solid-state storage manages a mapping or translation table and performs various duties to manage the user data in the flash memory.

FIG. 1 is a perspective view of a storage cluster 160, with multiple storage nodes 150 and internal solid-state memory coupled to each storage node to provide network attached storage or storage area network, in accordance with some embodiments. A network attached storage, storage area network, or a storage cluster, or other storage memory, could include one or more storage clusters 160, each having one or more storage nodes 150, in a flexible and reconfigurable arrangement of both the physical components and the amount of storage memory provided thereby. The storage cluster 160 is designed to fit in a rack, and one or more racks can be set up and populated as desired for the storage memory. The storage cluster 160 has a single chassis 138 having multiple slots 142. It should be appreciated that chassis 138 may be referred to as a housing, enclosure, or rack unit. In one embodiment, the chassis 138 has fourteen slots 142, although other numbers of slots are readily devised. For example, some embodiments have four slots, eight slots, sixteen slots, thirty-two slots, or other suitable number of slots. Each slot 142 can accommodate one storage node 150 in some embodiments. Chassis 138 includes flaps 148 that can be utilized to mount the chassis 138 on a rack. Fans 144 provide air circulation for cooling of the storage nodes 150 and components thereof, although other cooling components could be used, or an embodiment could be devised without cooling components. A switch fabric 146 couples storage nodes 150 within chassis 138 together and to a network for communication to the memory. In an embodiment depicted in FIG. 1, the slots 142 to the left of the switch fabric 146 and fans 144 are shown occupied by storage nodes 150, while the slots 142 to the right of the switch fabric 146 and fans 144 are empty and available for insertion of storage node 150 for illustrative purposes. This configuration is one example, and one or more storage nodes 150 could occupy the slots 142 in various further arrangements. The storage node arrangements need not be sequential or adjacent in some embodiments. Storage nodes 150 are hot pluggable, meaning that a storage node 150 can be inserted into a slot 142 in the chassis 138, or removed from a slot 142, without stopping or powering down the system. Upon insertion or removal of storage node 150 from slot 142, the system automatically reconfigures in order to recognize and adapt to the change. Reconfiguration, in some embodiments, includes restoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodiment shown here, the storage node 150 includes a printed circuit board 158 populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU 156, and a non-volatile solid state storage 152 coupled to the CPU 156, although other mountings and/or components could be used in further embodiments. The memory 154 has instructions which are executed by the CPU 156 and/or data operated on by the CPU 156. As further explained below, the non-volatile solid state storage 152 includes flash or, in further embodiments, other types of solid-state memory.

Storage cluster 160 is scalable, meaning that storage capacity with non-uniform storage sizes is readily added, as described above. One or more storage nodes 150 can be plugged into or removed from each chassis and the storage cluster self-configures in some embodiments. Plug-in storage nodes 150, whether installed in a chassis as delivered or later added, can have different sizes. For example, in one embodiment a storage node 150 can have any multiple of 4 TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, a storage node 150 could have any multiple of other storage amounts or capacities. Storage capacity of each storage node 150 is broadcast, and influences decisions of how to stripe the data. For maximum storage efficiency, an embodiment can self-configure as wide as possible in the stripe, subject to a predetermined requirement of continued operation with loss of up to one, or up to two, non-volatile solid state storage units 152 or storage nodes 150 within the chassis.

FIG. 2 is a system diagram of an enterprise computing system 102, which can use one or more of the storage nodes, storage clusters and/or non-volatile solid-state storage of FIG. 1 as a storage resource 108. For example, flash storage 128 of FIG. 2 may integrate the storage nodes, storage clusters and/or non-volatile solid-state storage of FIG. 1 in some embodiments. The enterprise computing system 102 has processing resources 104, networking resources 106 and storage resources 108, including flash storage 128. A flash controller 130 and flash memory 132 are included in the flash storage 128. In various embodiments, the flash storage 128 could include one or more storage nodes or storage clusters, with the flash controller 130 including the CPUs, and the flash memory 132 including the non-volatile solid-state storage of the storage nodes. In some embodiments flash memory 132 may include different types of flash memory or the same type of flash memory. The enterprise computing system 102 illustrates an environment suitable for deployment of the flash storage 128, although the flash storage 128 could be used in other computing systems or devices, larger or smaller, or in variations of the enterprise computing system 102, with fewer or additional resources. The enterprise computing system 102 can be coupled to a network 140, such as the Internet, in order to provide or make use of services. For example, the enterprise computing system 102 could provide cloud services, physical computing resources, or virtual computing services.

In the enterprise computing system 102, various resources are arranged and managed by various controllers. A processing controller 110 manages the processing resources 104, which include processors 116 and random-access memory (RAM) 118. Networking controller 112 manages the networking resources 106, which include routers 120, switches 122, and servers 124. A storage controller 114 manages storage resources 108, which include hard drives 126 and flash storage 128. Other types of processing resources, networking resources, and storage resources could be included with the embodiments. In some embodiments, the flash storage 128 completely replaces the hard drives 126. The enterprise computing system 102 can provide or allocate the various resources as physical computing resources, or in variations, as virtual computing resources supported by physical computing resources. For example, the various resources could be implemented using one or more servers executing software. Files or data objects, or other forms of data, are stored in the storage resources 108.

In various embodiments, an enterprise computing system 102 could include multiple racks populated by storage clusters, and these could be located in a single physical location such as in a cluster or a server farm. In other embodiments the multiple racks could be located at multiple physical locations such as in various cities, states or countries, connected by a network. Each of the racks, each of the storage clusters, each of the storage nodes, and each of the non-volatile solid-state storage could be individually configured with a respective amount of storage space, which is then reconfigurable independently of the others. Storage capacity can thus be flexibly added, upgraded, subtracted, recovered and/or reconfigured at each of the non-volatile solid-state storages. As mentioned previously, each storage node could implement one or more servers in some embodiments.

FIG. 3 is a multiple level block diagram, showing contents of a storage node 150 and contents of a non-volatile solid state storage 152 of the storage node 150. Data is communicated to and from the storage node 150 by a network interface controller (NIC) 202 in some embodiments. Each storage node 150 has a CPU 156, and one or more non-volatile solid state storage 152, as discussed above. Moving down one level in FIG. 3, each non-volatile solid state storage 152 has a relatively fast non-volatile solid state memory, such as nonvolatile random access memory (NVRAM) 204, and flash memory 206. In some embodiments, NVRAM 204 may be a component that does not require program/erase cycles (DRAM, MRAM, PCM), and can be a memory that can support being written vastly more often than the memory is read from. Moving down another level in FIG. 3, the NVRAM 204 is implemented in one embodiment as high speed volatile memory, such as dynamic random access memory (DRAM) 216, backed up by energy reserve 218. Energy reserve 218 provides sufficient electrical power to keep the DRAM 216 powered long enough for contents to be transferred to the flash memory 206 in the event of power failure. In some embodiments, energy reserve 218 is a capacitor, super-capacitor, battery, or other device, that supplies a suitable supply of energy sufficient to enable the transfer of the contents of DRAM 216 to a stable storage medium in the case of power loss. The flash memory 206 is implemented as multiple flash dies 222, which may be referred to as packages of flash dies 222 or an array of flash dies 222. It should be appreciated that the flash dies 222 could be packaged in any number of ways, with a single die per package, multiple dies per package (i.e. multichip packages), in hybrid packages, as bare dies on a printed circuit board or other substrate, as encapsulated dies, etc. In the embodiment shown, the non-volatile solid state storage 152 has a controller 212 or other processor, and an input output (I/O) port 210 coupled to the controller 212. I/O port 210 is coupled to the CPU 156 and/or the network interface controller 202 of the flash storage node 150. Flash input output (I/O) port 220 is coupled to the flash dies 222, and a direct memory access unit (DMA) 214 is coupled to the controller 212, the DRAM 216 and the flash dies 222. In the embodiment shown, the I/O port 210, controller 212, DMA unit 214 and flash I/O port 220 are implemented on a programmable logic device (PLD) 208, e.g., a field programmable gate array (FPGA). In this embodiment, each flash die 222 has pages, organized as sixteen kB (kilobyte) pages 224, and a register 226 through which data can be written to or read from the flash die 222. In further embodiments, other types of solid-state memory are used in place of, or in addition to flash memory illustrated within flash die 222.

In NVRAM 204, redundancy is not organized by segments but instead by messages, where each message (128 bytes to 128 kB) establishes its own data stripe, in some embodiments. NVRAM is maintained at the same redundancy as segment storage and operates within the same storage node groups in some embodiments. Because messages are stored individually the stripe width is determined both by message size and the storage cluster configuration. Larger messages may be more efficiently stored as wider strips.

Two of the many tasks of the CPU 156 on a storage node 150 are to break up write data, and reassemble read data. When the system has determined that data is to be written, an authority for that data is located in one of the non-volatile solid-state storages 152. The authority may be embodied as metadata, including one or more lists such as lists of data segments which the nonvolatile solid-state storage 152 manages. When a segment ID for data is already determined the request to write is forwarded to the non-volatile solid-state storage 152 currently determined to be the host of the authority determined from the segment. The host CPU 156 of the storage node 150, on which the non-volatile solid-state storage 152 and corresponding authority reside, then breaks up or shards the data and transmits the data out to various non-volatile solid-state storage 152. The transmitted data is written as a data stripe in accordance with an erasure coding scheme. In some embodiments, data is requested to be pulled, and in other embodiments, data is pushed. In reverse, when data is read, the authority for the segment ID containing the data is located as described above. The host CPU 156 of the storage node 150 on which the non-volatile solid-state storage 152 and corresponding authority reside requests the data from the non-volatile solid-state storage and corresponding storage nodes pointed to by the authority. In some embodiments the data is read from flash storage as a data stripe. The host CPU 156 of storage node 150 then reassembles the read data, correcting any errors (if present) according to the appropriate erasure coding scheme, and forwards the reassembled data to the network. In further embodiments, some or all of these tasks can be handled in the non-volatile solid-state storage 152. In some embodiments, the segment host requests the data be sent to storage node 150 by requesting pages from storage and then sending the data to the storage node making the original request.

In some systems, for example in UNIX-style file systems, data is handled with an index node or inode, which specifies a data structure that represents an object in a file system. The object could be a file or a directory, for example. Metadata may accompany the object, as attributes such as permission data and a creation timestamp, among other attributes. A segment number could be assigned to all or a portion of such an object in a file system. In other systems, data segments are handled with a segment number assigned elsewhere. For purposes of discussion, the unit of distribution is an entity, and an entity can be a file, a directory or a segment. That is, entities are units of data or metadata stored by a storage system. Entities are grouped into sets called authorities. Each authority has an authority owner, which is a storage node that has the exclusive right to update the entities in the authority. In other words, a storage node contains the authority, and that the authority, in turn, contains entities.

A segment is a logical container of data in accordance with some embodiments. A segment may be an address space between medium address space and physical flash locations. Each data segment is protected, e.g., from memory and other failures, by breaking the segment into a number of data and parity shards, where applicable. The data and parity shards are distributed, i.e., striped, across non-volatile solid-state storages 152 coupled to the host CPUs 156 in accordance with an erasure coding scheme. Usage of the term segments refers to the container and its place in the address space of segments in some embodiments. Usage of the term stripe refers to the same set of shards as a segment and includes how the shards are distributed along with redundancy or parity information in accordance with some embodiments.

A series of address-space transformations takes place across an entire storage system. At the top is the inode address space, which the filesystem uses to translate file paths to inode IDs (Identifications). Inodes point into medium address space, where data is logically stored. Medium addresses are mapped into segment address space. Segment addresses are then translated into physical flash locations. Physical flash locations have an address range bounded by the amount of flash in the system in accordance with some embodiments. Medium addresses and segment addresses are logical containers, and in some embodiments use a 128 bit or larger identifier so as to be practically infinite, with a likelihood of reuse calculated as longer than the expected life of the system. Addresses from logical containers are allocated in a hierarchical fashion in some embodiments. Initially, each non-volatile solid-state storage 152 may be assigned a range of address space. Within this assigned range, the non-volatile solid-state storage 152 is able to allocate addresses without synchronization with other non-volatile solid-state storage 152.

Data and metadata are stored by a set of underlying storage layouts that are optimized for varying workload patterns and storage devices. These layouts incorporate multiple redundancy schemes, compression formats and index algorithms. Some of these layouts store information about authorities and authority masters, while others store file metadata and file data. The redundancy schemes include error correction codes that tolerate corrupted bits within a single storage device (such as a NAND flash chip), erasure codes that tolerate the failure of multiple storage nodes, and replication schemes that tolerate data center or regional failures. In some embodiments, low density parity check (LDPC) code is used within a single storage unit. Data is not further replicated within a storage cluster, as it is assumed a storage cluster may fail. Reed-Solomon encoding is used within a storage cluster, and mirroring is used within a storage grid in some embodiments. Metadata may be stored using an ordered log structured index (such as a Log Structured Merge Tree), and large data may be stored in an unordered log structured layout (similar to log structured file systems).

FIG. 4 is a block diagram showing a communication path 234 for redundant copies of metadata 230, with further details of flash storage nodes 150 (i.e., storage nodes 150 having flash memory) and non-volatile solid-state storages 152 in accordance with some embodiments. Metadata 230 includes information about the user data that is written to or read from the flash memory 206. Metadata 230 can include messages, or derivations from the messages, indicating actions to be taken or actions that have taken place involving the data that is written to or read from the flash memory 206. Distributing redundant copies of metadata 230 to the non-volatile solid-state storage units 152 through the communication interconnect 170 ensures that messages are persisted and can survive various types of failure the system may experience. Each non-volatile solid-state storage 152 dedicates a portion of the NVRAM 204 to storing metadata 230. In some embodiments, redundant copies of metadata 230 are stored in the additional non-volatile solid-state storage 152.

Flash storage nodes 150 are coupled via the communication interconnect 170. More specifically, the network interface controller 202 of each storage node 150 in the storage cluster is coupled to the communication interconnect 170, providing a communication path 234 among storage nodes 150 and non-volatile solid-state storage 152. Storage nodes 150 have one or more non-volatile solid-state storage units 152. Non-volatile solid-state storage units 152 internal to a storage node can communicate with each other, for example via a bus, a serial communication path, a network path or other communication path 234 as readily devised in accordance with the embodiments disclosed herein. Communication interconnect 170 can be included in or implemented with the switch fabric of FIG. 1 in some embodiments. Storage nodes 150 of FIG. 4 form a storage cluster that is enclosed within a single chassis that has an internal power distribution bus within the chassis as described with reference to FIG. 1.

Referring to FIGS. 3 and 4, in case of a power failure, whether local to non-volatile solid-state storage 152 or a storage node 150, data can be copied from the NVRAM 204 to the flash memory 206. For example, the DMA unit 214 of FIG. 3 can copy contents of the NVRAM 204, including the metadata, to the flash memory 206, using power supplied by the energy reserve 218. Energy reserve 218 is sized with sufficient capacity to support copy operation. That is, the energy reserve 218 should be sized so as to provide sufficient current at a sufficient voltage level for a time duration long enough to complete the copying so that messages that are in metadata 230 are persisted in the flash memory 206.

A further mechanism for persisting messages in a storage system involves the communication path 234 described above in FIG. 4. Redundant copies of the metadata 230 can be distributed via the communication path 234, in various ways. For example, a message coming from the filesystem could be distributed via the communication interconnect 170 as a broadcast over the communication path 234 to all of the non-volatile solid-state storages 152. A non-volatile solid-state storage 152 could send a copy of metadata 230 over the communication path 234 to other non-volatile solid-state storage 152 in a storage node 150. CPU 156 on a storage node 150, receiving a message from the communication interconnect 170 via the network interface controller 202 could send a copy of the message to each solid-state storage 152. The CPU 156 may rebroadcast the message to other flash storage nodes 150, and the flash storage nodes 150 could then distribute the message to the solid-state storages 152 in each of these flash storage nodes 150 in some embodiments. In these and other uses of the communication path 234, redundant copies of the metadata 230 can be distributed to the non-volatile solid-state storages 152. Then, if one non-volatile solid-state storage 152, or one storage node 150 experiences a failure, redundant copies of any message are available in metadata 230 of at least one other non-volatile solid-state storage 152. Each non-volatile solid-state storage 152 can apply decision logic 232 when evaluating various situations such as local power failure, an unreachable node, or instructions to consider or commence a data recovery or a data rebuild. The decision logic 232 includes witnessing logic, voting logic, consensus logic and/or other types of decision logic in various embodiments. Decision logic 232 could be implemented in hardware, software executing on the controller 212, firmware, or combinations thereof, and could be implemented as part of the controller 212 or coupled to the controller 212. The decision logic 232 is employed in consensus decisions among multiple solid-state storage units 152, in some embodiments. In further embodiments, the decision logic 232 could cooperate with the other non-volatile solid-state storage units 152 in order to gather copies of the redundant metadata 230, and make local decisions. The mechanisms for persisting messages in a storage system are useful in the event of a failure, and can be used in data recovery and reconstruction as described above.

Examples of messages include a request to write data, a request to read data, a request to lock or unlock a file, a change in permission of a file, an update to a file allocation table or other file or directory structure, a request to write a file that has executable instructions or to write a file name that is reserved and interpreted as an executable direction, updates to one or more authorities, updates to a fingerprint table, list or other data used in deduplication, updates to hash tables, updates to logs, and so on. When a message is received in non-volatile solid-state storage 152 of a storage node 150, indicating some action has taken place, the message or a derivation of the message is stored as metadata 230 in the NVRAM 204 of that solid-state storage 152. By applying the redundant copies of the metadata 230, actions are captured that are in progress, so that if a failure happens, these actions can be replayed and replacement actions can then be performed, for example upon restart. Actions span storage nodes and use cluster messaging, so the act of sending a message can be made persistent data via one or more of the mechanisms for persisting messages. These mechanisms address some of the known failure scenarios in order to ensure availability of data. In some embodiments, the messages don't require permanence beyond completion of the actions. In other embodiments the messages are further retained to facilitate rollback or other recovery operations.

For example, if a command is sent out to carry out a write operation, this message is recorded and redundant. If there is a failure, it can be determined whether or not that action has been carried out, and whether or not the action should be driven to completion. Such determination can be carried out using the decision logic 232 in each non-volatile solid-state storage 152. There is dedicated storage in NVRAM 204 for messages and other metadata 230, so that messages are recorded in the non-volatile solid-state storage 152 and replicated in some embodiments. The messages and other metadata 230 are written into flash memory 206 if one non-volatile solid-state storage 152 experiences a power failure, or if the entire system experiences a power failure or otherwise shuts down. The redundancy level of the messages matches the redundancy level of the metadata in some embodiments. When there are sufficient numbers of copies of messages, the message becomes irrevocable. If one node goes down, other nodes can vote, achieve consensus, or witness the various copies of the message and determine what action, if any, to carry to completion. If the entire system goes down, e.g., through a global power failure, then a sufficient number of these messages get written from NVRAM 204 to flash memory 206. Upon restoration of power, the nodes can again open copies of the message and determine what action, if any, to carry to completion to prevent any corruption.

With continued reference to FIGS. 3 and 4, storage node 150 of a storage cluster 160 includes two levels of controllers. There is a host CPU 156 in the storage node 150, and there is a controller 212 in the non-volatile solid-state storage 152. The controller 212 can be considered a flash memory controller, which serves as a bridge between the host CPU 156 and the flash memory 206. Each of these controllers, namely the host CPU 156 and the flash controller 212, can be implemented as one or more processors or controllers of various types from various manufacturers. The host CPU 156 can access both the flash memory 206 and the NVRAM 204 as distinct resources, with each being independently (i.e., individually) addressable by the host CPU 156.

By separating the NVRAM 204 and the flash memory 206 into distinct resources, not all data placed in the NVRAM 204 must be written to the flash memory 206. The NVRAM 204 can also be employed for various functions and purposes. For example, updates to the NVRAM 204 can be made obsolete by newer updates to the NVRAM 204. A later transfer of user data from the NVRAM 204 to the flash memory 206 can transfer the updated user data, without transferring the obsolete user data to the flash memory 206. This reduces the number of erasure cycles of the flash memory 206, reduces wear on the flash memory 206, and moves data more efficiently. The CPU 156 can write to the NVRAM 204 at a smaller granularity than the granularity of the transfers from the NVRAM 204 to the flash memory 206. For example, the CPU 156 could perform 4 kB writes to the NVRAM 204, and the DMA unit 214 could perform a page write of 16 kB from the NVRAM 204 to the flash memory 206 under direction of the controller 212. The ability to collect multiple writes of user data to the NVRAM 204 prior to writing the user data from the NVRAM 204 to the flash memory 206 increases writing efficiency. In some embodiments, a client write of user data is acknowledged at the point at which the user data is written to the NVRAM 204. Since the energy reserve 218, described above with reference to FIG. 3, provides sufficient power for a transfer of contents of the NVRAM 204 to the flash memory 206, the acknowledgment of the client write does not need to wait until the user data is written to the flash memory 206.

As further examples of differences between present embodiments and previous solid-state drives, the metadata 230 in the NVRAM 204 is not written into the flash memory 206, except in cases of power loss. Here, a portion of the NVRAM 204 acts as a workspace for the CPU 156 of the storage node 150 to apply the metadata 230. The CPU 156 of the storage node 150 can write to the NVRAM 204 and read the NVRAM 204, in order to access the metadata 230. The CPU 156 is responsible for migrating data from the NVRAM 204 down to the flash memory 206 in one embodiment. Transfer from the NVRAM 204 to the flash memory 206 is not automatic and predetermined, in such embodiments. Transfer waits until there is sufficient user data in the NVRAM 204 for a page write to the flash memory 206, as determined by the CPU 156 and directed to the DMA unit 214. The DMA unit 214 can be further involved in the path of the user data. In some embodiments, the DMA unit 214 (also known as a DMA engine) is designed to detect and understand various data formats. The DMA unit 214 can perform a cyclic redundancy check (CRC) calculation to check the integrity of the user data. In some embodiments, the DMA unit 214 inserts the CRC calculation into the data and verifies that the data is consistent with a previously inserted CRC calculation.

Work may be offloaded to the controller 212 of the non-volatile solid-state storage 152. Processing that is offloaded to flash controller 212 can be co-designed with processing performed by the CPU 156 of the storage node 150. Various mapping tables that translate from one address space to another, e.g., index trees or address translation tables, can be managed within the non-volatile solid-state storage 152, in some embodiments. The controller 212 of the non-volatile solid-state storage 152 can perform various tasks such as looking through these mapping tables, finding metadata associated with the mapping tables, and determining physical addresses, e.g., for user data sought by the CPU 156 of the storage node 150. In order to find an authority associated with a segment number, a standard solid-state drive might bring back an entire 16 kB flash page, and the CPU 156 would search in this page. In some embodiments, the controller 212 of the non-volatile solid-state storage 152 can perform this search much more efficiently, and pass the results to the CPU 156 of the storage node 150, without sending back the entire flash page to the CPU 156.

FIG. 5 is a flow diagram of a method for accessing a non-volatile solid-state storage, which can be practiced on or by embodiments of storage clusters, storage nodes and/or non-volatile solid-state storages in accordance with some embodiments. Many of the actions described in the method can be performed by one or more processors, such as processors on storage nodes and non-volatile solid-state storages in some embodiments. In an action 502, user data is sent to a storage cluster. For example, a client could send the user data via a network, for storage in the storage cluster. The user data is forwarded to a storage node, in an action 504. For example, the storage cluster could route the user data to a storage node via a communication interconnect. In an action 506, the user data is written from the storage node into NVRAM of a non-volatile solid-state storage. For example, a CPU of the storage node could write the user data from the storage node into the NVRAM of a non-volatile solid-state storage. The client write is acknowledged, in an action 508. For example, the CPU of the storage node acknowledges the client write.

Metadata is written into the NVRAM of the non-volatile solid-state storage, in an action 510. For example, the CPU of the storage node could write metadata pertaining to user data into the NVRAM of the non-volatile solid-state storage. In a decision action 512, it is determined if there is sufficient user data in the NVRAM for a batch mode transfer from the NVRAM to flash memory of the non-volatile solid-state storage. If the answer is no, flow branches back to the action 502, for more user data. If the answer is yes, flow continues to the action 514.

The controller of the non-volatile solid-state storage is directed to perform the transfer, in an action 514. For example, the CPU of the storage node could direct the controller of the non-volatile solid-state storage to perform a page write or other batch mode transfer, since there is now sufficient user data in the NVRAM. The DMA unit is directed to perform the transfer, in an action 516. For example, upon receiving instructions from the CPU of the storage node, the controller may direct the DMA unit of the non-volatile solid-state storage to perform a DMA transfer of the user data from the NVRAM to the flash memory. The user data is transferred from the NVRAM of the non-volatile solid-state storage to the flash memory of the non-volatile solid-state storage, in an action 518. This transfer could be performed by the DMA unit, as directed by the controller.

Metadata is read from the NVRAM of the non-volatile solid-state storage, in an action 520. For example, the CPU of the storage node could read the metadata from the NVRAM, in order to obtain information pertaining to the user data. In an action 522, the controller of the non-volatile solid-state storage is requested to find information in the flash memory of the non-volatile solid-state storage. For example, the CPU of the storage node, after processing the metadata obtained from the NVRAM, could request the controller of the non-volatile solid-state storage find additional information.

In an action 524, the information within the flash memory is searched. For example, the controller of the non-volatile solid-state storage could read a page from the flash memory, and search for the information. The information is sent to the CPU of the storage node, in an action 526. For example, the controller of the non-volatile solid-state storage could find the information in a subset of the page of the flash memory, and send the information to the CPU of the storage node, without sending the entire page. The CPU of the storage node could then use this information, perhaps in combination with the metadata that the CPU read from the NVRAM to locate user data for reading. In other embodiments the information could be used to determine a location for writing user data or performing other operations as readily devised in accordance with the teachings herein.

It should be appreciated that the methods described herein may be performed with a digital processing system, such as a conventional, general-purpose computer system. Special purpose computers, which are designed or programmed to perform only one function may be used in the alternative. FIG. 6 is an illustration showing an exemplary computing device which may implement the embodiments described herein. The computing device of FIG. 6 may be used to perform embodiments of the functionality for a storage node or a non-volatile solid-state storage in accordance with some embodiments. The computing device includes a central processing unit (CPU) 601, which is coupled through a bus 605 to a memory 603, and mass storage device 607. Mass storage device 607 represents a persistent data storage device such as a disc drive, which may be local or remote in some embodiments. The mass storage device 607 could implement a backup storage, in some embodiments. Memory 603 may include read only memory, random access memory, etc. Applications resident on the computing device may be stored on or accessed via a computer readable medium such as memory 603 or mass storage device 607 in some embodiments. Applications may also be in the form of modulated electronic signals modulated accessed via a network modem or other network interface of the computing device. It should be appreciated that CPU 601 may be embodied in a general-purpose processor, a special purpose processor, or a specially programmed logic device in some embodiments.

Display 611 is in communication with CPU 601, memory 603, and mass storage device 607, through bus 605. Display 611 is configured to display any visualization tools or reports associated with the system described herein. Input/output device 609 is coupled to bus 605 in order to communicate information in command selections to CPU 601. It should be appreciated that data to and from external devices may be communicated through the input/output device 609. CPU 601 can be defined to execute the functionality described herein to enable the functionality described with reference to FIGS. 1-5. The code embodying this functionality may be stored within memory 603 or mass storage device 607 for execution by a processor such as CPU 601 in some embodiments. The operating system on the computing device may be MS-WINDOWS™, UNIX™, LINUX™, iOS™, CentOS™, Android™, Redhat Linux™, z/OS™, or other known operating systems. It should be appreciated that the embodiments described herein may be integrated with virtualized computing system also.

Detailed illustrative embodiments are disclosed herein. However, specific functional details disclosed herein are merely representative for purposes of describing embodiments. Embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one step or calculation from another. For example, a first calculation could be termed a second calculation, and, similarly, a second step could be termed a first step, without departing from the scope of this disclosure. As used herein, the term “and/or” and the “/” symbol includes any and all combinations of one or more of the associated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

With the above embodiments in mind, it should be understood that the embodiments might employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. Further, the manipulations performed are often referred to in terms, such as producing, identifying, determining, or comparing. Any of the operations described herein that form part of the embodiments are useful machine operations. The embodiments also relate to a device or an apparatus for performing these operations. The apparatus can be specially constructed for the required purpose, or the apparatus can be a general-purpose computer selectively activated or configured by a computer program stored in the computer. In particular, various general-purpose machines can be used with computer programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform the required operations.

A module, an application, a layer, an agent or other method-operable entity could be implemented as hardware, firmware, or a processor executing software, or combinations thereof. It should be appreciated that, where a software-based embodiment is disclosed herein, the software can be embodied in a physical machine such as a controller. For example, a controller could include a first module and a second module. A controller could be configured to perform various actions, e.g., of a method, an application, a layer or an agent.

The embodiments can also be embodied as computer readable code on a non-transitory computer readable medium. The computer readable medium is any data storage device that can store data, which can be thereafter read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and other optical and non-optical data storage devices. The computer readable medium can also be distributed over a network coupled computer system so that the computer readable code is stored and executed in a distributed fashion. Embodiments described herein may be practiced with various computer system configurations including hand-held devices, tablets, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers and the like. The embodiments can also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a wire-based or wireless network.

Although the method operations were described in a specific order, it should be understood that other operations may be performed in between described operations, described operations may be adjusted so that they occur at slightly different times or the described operations may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing.

In various embodiments, one or more portions of the methods and mechanisms described herein may form part of a cloud-computing environment. In such embodiments, resources may be provided over the Internet as services according to one or more various models. Such models may include Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). In IaaS, computer infrastructure is delivered as a service. In such a case, the computing equipment is generally owned and operated by the service provider. In the PaaS model, software tools and underlying equipment used by developers to develop software solutions may be provided as a service and hosted by the service provider. SaaS typically includes a service provider licensing software as a service on demand. The service provider may host the software, or may deploy the software to a customer for a given period of time. Numerous combinations of the above models are possible and are contemplated.

Various units, circuits, or other components may be described or claimed as “configured to” perform a task or tasks. In such contexts, the phrase “configured to” is used to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry) that performs the task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. 112, sixth paragraph, for that unit/circuit/component. Additionally, “configured to” can include generic structure (e.g., generic circuitry) that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the task(s) at issue. “Configured to” may also include adapting a manufacturing process (e.g., a semiconductor fabrication facility) to fabricate devices (e.g., integrated circuits) that are adapted to implement or perform one or more tasks.

The foregoing description, for the purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the embodiments and its practical applications, to thereby enable others skilled in the art to best utilize the embodiments and various modifications as may be suited to the particular use contemplated. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims. 

What is claimed is:
 1. A method of operating a storage unit, performed by the storage unit, comprising: receiving metadata from one of a plurality of storage nodes of a storage cluster; writing the metadata into nonvolatile random-access memory (NVRAM) of the storage unit; sending redundant copies of the metadata to further storage units, in the storage cluster; receiving erasure coded data from the one of the plurality of storage nodes into the NVRAM; and writing the erasure coded data from the NVRAM into solid-state storage memory of the storage unit.
 2. The method of claim 1, further comprising: supporting the NVRAM with a power reserve, in case of a power loss, and wherein the storage cluster is contained within multiple chassis.
 3. The method of claim 1, further comprising: transferring the metadata and the erasure coded data from the NVRAM into the solid-state storage memory, responsive to a power loss.
 4. The method of claim 1, further comprising: supporting access to the NVRAM by both a processor of the storage unit and a processor of the one of the plurality of storage nodes in the storage cluster.
 5. The method of claim 1, further comprising: supporting addressability of both the NVRAM and the solid-state storage memory by a processor of the one of the plurality of storage nodes in the storage cluster as distinct resources.
 6. The method of claim 1, further comprising: receiving multiple writes of erasure coded data into the NVRAM; and writing data of the multiple writes of erasure coded data from the NVRAM into the solid-state storage memory in a batch mode.
 7. The method of claim 1, further comprising: finding metadata associated with a mapping table; and determining a physical address for user data sought by a processor of one of the plurality of storage nodes in the storage cluster, based on the metadata associated with the mapping table.
 8. A tangible, non-transitory, computer-readable media having instructions thereupon which, when executed by a processor, cause the processor to perform a method comprising: writing metadata received from one of a plurality of storage nodes in a storage cluster into nonvolatile random-access memory (NVRAM) of a storage unit in the storage cluster; sending redundant copies of the metadata from the storage unit to further storage units, in the storage cluster; writing erasure coded data received from the one of the plurality of storage nodes into the NVRAM in the storage unit; and writing the erasure coded data from the NVRAM of the storage unit into solid-state storage memory of the storage unit.
 9. The computer-readable media of claim 8, wherein the method further comprises: writing the metadata and the erasure coded data or further erasure coded data from the NVRAM into the solid-state storage memory, responsive to loss of power, and wherein the storage cluster is contained within multiple chassis.
 10. The computer-readable media of claim 8, wherein the method further comprises: receiving, at the storage unit, a message to access the NVRAM, from one of the plurality of storage nodes; accessing the NVRAM, responsive to receiving the message; and sending a further message from the storage unit to the one of the plurality of storage nodes, responsive to the accessing the NVRAM.
 11. The computer-readable media of claim 8, wherein the method further comprises: receiving, at the storage unit, a message to access the NVRAM, from the one of the plurality of storage nodes; accessing the NVRAM, responsive to receiving the message; receiving at the storage unit, a further message to access the solid-state storage memory, from the one of the plurality of storage nodes or a further one of the plurality of storage nodes; and accessing the solid-state storage memory, responsive to receiving the further message.
 12. The computer-readable media of claim 8, wherein the method further comprises: receiving a plurality of writes of erasure coded data into the NVRAM; and writing data from the plurality of writes of erasure coded data from the NVRAM into the solid-state storage memory, as a batch write.
 13. The computer-readable media of claim 8, wherein the method further comprises: receiving a request from a further one of the plurality of storage nodes, for user data; finding metadata associated with a mapping table, in the NVRAM; and determining a physical address of the solid-state storage memory for the user data, based on the metadata associated with the mapping table.
 14. A storage unit, comprising: solid-state storage memory; nonvolatile random-access memory (NVRAM); a processor, configurable to cooperate with processors of storage nodes in a storage cluster and processors of further storage units in the storage cluster, to receive metadata from one or more of the storage nodes into the NVRAM and distribute redundant copies of the metadata to the further storage units; and the processor further configurable to receive erasure coded data from the one or more storage nodes into the NVRAM and write the erasure coded data from the NVRAM into the solid-state storage memory.
 15. The storage unit of claim 14, wherein the NVRAM comprises DRAM (dynamic random access memory) and a power reserve, and wherein the storage cluster is contained within multiple chassis.
 16. The storage unit of claim 14, further comprising: the processor further configurable to flush the metadata and the erasure coded data from the NVRAM into the solid-state storage memory, responsive to a power loss.
 17. The storage unit of claim 14, wherein the NVRAM is accessible by both the processor of the storage unit and a processor of one of the storage nodes in the storage cluster.
 18. The storage unit of claim 14, wherein both the NVRAM and the solid-state storage memory are addressable by a processor of one of the storage nodes in the storage cluster as distinct resources.
 19. The storage unit of claim 14, wherein the processor is further configurable to receive multiple writes of the erasure coded data prior to writing the erasure coded data from the NVRAM into the solid-state storage memory in a batch.
 20. The storage unit of claim 14, further comprising: the processor further configurable to find metadata associated with a mapping table and determine a physical address for user data sought by a processor of one of the storage nodes in the storage cluster. 